246 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



represent the final opinions of Dr. Gidley. I have, however, quoted 

 parts of the manuscript directly, have mentioned some other of Dr. 

 Gidley's opinions in indirect quotation, and have used his manuscript 

 names and followed his disposition of the specimens as far as possible. 



The material has been much increased since Dr. Gidley's study of 

 it, but it is still rare. He tentatively identified only 8 specimens, and 

 1 1 have since been collected (3 for the National Museum and 8 for the 

 American Museum). This family is abundant in the Torrejon, and 

 also in the lower Eocene, but it is extremely rare in the quarries in 

 the Crazy Mountain Field and can be considered as common only at 

 one surface locality, no. 25, from which 11 specimens have been 

 obtained. 



In the Torrejon the only genus of this family is Tetraclaenodon} 

 It is there very abundant and highly varied and has therefore received 

 numerous specific names, but from Matthew's work it seems probable 

 that only two valid species occur in the Torrejon: Tetraclaenodon 

 jjuercensis, a larger, more common, and varied form, and T. pliciferus, 

 a smaller, rarer, and perhaps less varied species. 



In the Crazy Mountain Field, also, there are indications of two 

 species, one of about the size of T. puercensis, but very rare and not 

 exactly identifiable, the other smaller, although generally larger than 

 T. pliciferus. There is also a second genus, Gidleyina, apparently 

 characteristic of the higher levels in this field. 



TETRACLAENODON Scott, 1892 



TETRACLAENODON SYMBOLICUS Gidley 



FiGUKES 70, 71 

 Tetraclaenodon symbolicus Gidley, Simpson, 1935d, p. 239. 



Type. — U.S.N. M. no. 6169, part of right lower jaw wdth Mj and 

 alveoh of P3.4 and M2. Collected by A. C. Silberling.^ 



Paratype. — U.S.N.M. no. 6168, jaw fragment with right Mi_2, and 

 a separate left P4 probably this species but probably not associated. 

 Collected by A. C. Silberling. 



' This genus is still often called Euprotogonia. It was originally described as Protogonia Cope, 1881. Cope 

 later considered this as preoccupied by Protogonius Hiibner, 1816, and replaced it by Euprotogonia Cope, 

 1893, the type of both being P. (or E.) subguadrata. In the meantime Scott had proposed the genus Tetra- 

 claenodon Scott, 1892, for Mioctaenus floverianu-i Cope. Scott did not recognize the relationship, but his 

 Tetraclaenodon was certainly the same genus as Protogonia Cope, and it therefore includes as a synonym 

 Euprotogonia Cope. Matthew in 1897 preferred Euprotogonia Cope, 1893, to Tetraclaenodon Scott, 1892, on 

 the ground that the latter was based on an error, and through Matthew's work Euprotogonia became the 

 familiar name for the genus. Matthew later recognized that his action had been invalid, and he used the 

 name Tetraclaenodon in all his more recent worls. Now Cabrera (1935) has insisted that Protogonius Hiibner 

 does not preoccupy Protogonia Cope, since they differ in termination, and he calls the genus Protogonia. 

 Without taking a decisive stand, I shall tentatively continue to use Tetraclaenodon, which has the cardinal 

 virtue of being generally and correctly understood and of being unambiguous. Euprotogonia is certainly 

 invalid, and Protogonia is of dubious validity, is ambiguous, and is unfamiliar to present-day students. 



' I retain this specimen as type, since it is clearly that intended by Qidley. No. 6168, here made paratype, 

 would be a better type. 



